Serum insulin-like growth factor-I and amyloid beta protein in Alzheimer's disease: relationship with cognitive function

The Associations Between Serum Insulin-like Growth Factor-I, Brain White Matter Volumes, and Cognition in Mild Cognitive Impairment and Alzheimer's Disease

Background

Insulin-like growth factor-I (IGF-I) regulates myelin, but little is known whether IGF-I associates with white matter functions in subjective and objective mild cognitive impairment (SCI/MCI) or Alzheimer's disease (AD).

Objective

To explore whether serum IGF-I is associated with magnetic resonance imaging - estimated brain white matter volumes or cognitive functions.

Methods

In a prospective study of SCI/MCI (n = 106) and AD (n = 59), we evaluated the volumes of the total white matter, corpus callosum (CC), and white matter hyperintensities (WMHs) as well as Mini-Mental State Examination (MMSE), Trail Making Test A and B (TMT-A/B), and Stroop tests I-III at baseline, and after 2 years.

Results

IGF-I was comparable in SCI/MCI and AD (113 versus 118 ng/mL, p = 0.44). In SCI/MCI patients, the correlations between higher baseline IGF-I and greater baseline and 2-year volumes of the total white matter and total CC lost statistical significance after adjustment for intracranial volume and other covariates. However, after adjustment for covariates, higher baseline IGF-I correlated with better baseline scores of MMSE and Stroop test II in SCI/MCI and with better baseline results of TMT-B and Stroop test I in AD. IGF-I did not correlate with WMH volumes or changes in any of the variables.

Conclusions

Both in SCI/MCI and AD, higher IGF-I was associated with better attention/executive functions at baseline after adjustment for covariates. Furthermore, the baseline associations between IGF-I and neuropsychological test results in AD may argue against significant IGF-I resistance in the AD brain.

Insulin resistance, cognition, and Alzheimer disease

Chronic diseases of aging are increasingly common. Dementia, often due to multiple etiologies including Alzheimer disease (AD), is at the forefront. Previous studies have reported higher rates of dementia among persons with diabetes, yet less is known about how insulin resistance relates to cognition. This article reviews recently published data on the relationship of insulin resistance to cognition and AD, and remaining knowledge gaps in the field are discussed. A structured review of studies was conducted over a 5-year period, investigating insulin and cognitive function in adults with a baseline mean age of ≥65 years. This search yielded 146 articles, of which 26 met the predetermined inclusion and exclusion criteria. Among the nine studies that specifically examined insulin resistance and cognitive dysfunction and/or decline, eight studies suggest an association, but some only in subanalyses. Results are mixed in studies relating insulin to structural and functional changes on brain imaging, and data on intranasal insulin for cognition remain unclear. Future avenues are proposed to elucidate the impact of insulin resistance on brain structure and function, including cognition, in persons with and without AD.

Identification of the molecular mechanism of insulin-like growth factor-1 (IGF-1): a promising therapeutic target for neurodegenerative diseases associated with metabolic syndrome

Neurodegenerative disorders are accompanied by neuronal degeneration and glial dysfunction, resulting in cognitive, psychomotor, and behavioral impairment. Multiple factors including genetic, environmental, metabolic, and oxidant overload contribute to disease progression. Recent evidences suggest that metabolic syndrome is linked to various neurodegenerative diseases. Metabolic syndrome (MetS) is known to be accompanied by symptoms such as hyperglycemia, abdominal obesity, hypertriglyceridemia, and hypertension. Despite advances in knowledge about the pathogenesis of neurodegenerative disorders, effective treatments to combat neurodegenerative disorders caused by MetS have not been developed to date. Insulin growth factor-1 (IGF-1) deficiency has been associated with MetS-related pathologies both in-vivo and in-vitro. IGF-1 is essential for embryonic and adult neurogenesis, neuronal plasticity, neurotropism, angiogenesis, metabolic function, and protein clearance in the brain. Here, we review the evidence for the potential therapeutic effects of IGF-1 in the neurodegeneration related to metabolic syndrome. We elucidate how IGF-1 may be involved in molecular signaling defects that occurs in MetS-related neurodegenerative disorders and highlight the importance of IGF-1 as a potential therapeutic target in MetS-related neurological diseases.

Correlation between parameters related to sarcopenia and gray matter volume in patients with mild to moderate Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disease characterized by brain atrophy and closely correlated with sarcopenia. Mounting studies indicate that parameters related to sarcopenia are associated with AD, but some results show inconsistent. Furthermore, the association between the parameters related to sarcopenia and gray matter volume (GMV) has rarely been explored.

AIM

To investigate the correlation between parameters related to sarcopenia and cerebral GMV in AD.

METHODS

Demographics, neuropsychological tests, parameters related to sarcopenia, and magnetic resonance imaging (MRI) scans were collected from 42 patients with AD and 40 normal controls (NC). Parameters related to sarcopenia include appendicular skeletal muscle mass index (ASMI), grip strength, 5-times sit-to-stand (5-STS) time and 6-m gait speed. The GMV of each cerebral region of interest (ROI) and the intracranial volume were calculated by computing the numbers of the voxels in the specific region based on MRI data. Partial correlation and multivariate stepwise linear regression analysis explored the correlation between different inter-group GMV ratios in ROIs and parameters related to sarcopenia, adjusting for covariates.

RESULTS

The 82 participants included 40 NC aged 70.13 ± 5.94 years, 24 mild AD patients aged 73.54 ± 8.27 years and 18 moderate AD patients aged 71.67 ± 9.39 years. Multivariate stepwise linear regression showed that 5-STS time and gait speed were correlated with bilateral hippocampus volume ratios in total AD. Grip strength was associated with the GMV ratio of the left middle frontal gyrus in mild AD and the GMV ratios of the right superior temporal gyrus and right hippocampus in moderate AD. However, ASMI did not have a relationship to any cerebral GMV ratio.

CONCLUSIONS

Among parameters related to sarcopenia, 5-STS time and gait speed were associated with bilateral hippocampus volume ratios at different clinical stages of patients with AD. Five-STS time provide an objective basis for early screening and can help diagnose patients with AD.

Roles and mechanisms of phospholipid transfer protein in the development of Alzheimer's disease

Phospholipid transfer protein (PLTP) is a complex glycosylated protein that mediates the transfer of phospholipids, unesterified cholesterol, diacylglycerides, specific apolipoproteins, and tocopherols between different classes of lipoproteins as well as between lipoproteins and cells. Many studies have associated PLTP with a variety of lipid metabolic diseases. However, recent studies have indicated that PLTP is highly expressed in the brain of vertebrate and may be related to many central nervous system diseases, such as Alzheimer's disease. Here, we review the data and report the role and mechanisms PLTP in Alzheimer's disease.

Alzheimer's Disease Susceptibility Gene Apolipoprotein E (APOE) and Blood Biomarkers in UK Biobank (N = 395,769)

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative condition where the underlying etiology is still unclear. Investigating the potential influence of apolipoprotein E (APOE), a major genetic risk factor, on common blood biomarkers could provide a greater understanding of the mechanisms of AD and dementia risk.

OBJECTIVE

Our objective was to conduct the largest (to date) single-protocol investigation of blood biomarkers in the context of APOE genotype, in UK Biobank.

METHODS

After quality control and exclusions, data on 395,769 participants of White European ancestry were available for analysis. Linear regressions were used to test potential associations between APOE genotypes and biomarkers.

RESULTS

Several biomarkers significantly associated with APOEɛ4 'risk' and ɛ2 'protective' genotypes (versus neutral ɛ3/ɛ3). Most associations supported previous data: for example, ɛ4 genotype was associated with elevated low-density lipoprotein cholesterol (LDL) (standardized beta [b] = 0.150 standard deviations [SDs] per allele, p < 0.001) and ɛ2 with lower LDL (b = -0.456 SDs, p < 0.001). There were however instances of associations found in unexpected directions: e.g., ɛ4 and increased insulin-like growth factor (IGF-1) (b = 0.017, p < 0.001) where lower levels have been previously suggested as an AD risk factor.

CONCLUSION

These findings highlight biomarker differences in non-demented people at genetic risk for dementia. The evidence herein supports previous hypotheses of involvement from cardiometabolic and neuroinflammatory pathways.

Patients with Alzheimer's Disease Have Increased Levels of Insulin-like Growth Factor-I in Serum but not in Cerebrospinal Fluid

BACKGROUND

Insulin-like growth factor-I (IGF-I) is important for amyloid-β (Aβ) metabolism, and also interacts with the brain vasculature. In previous IGF-I studies, it has not been evaluated whether Alzheimer's disease (AD) patients had vascular comorbidities.

OBJECTIVE AND METHODS

A cross-sectional study of 40 consecutive non-diabetic AD patients and 36 healthy controls. We measured IGF-I in serum and cerebrospinal fluid (CSF) and also serum insulin. Mixed forms of AD and vascular dementia were excluded.

RESULTS

After adjustment for covariates including age, serum IGF-I level was higher in the AD group than in the controls, whereas CSF IGF-I and serum insulin were unchanged. Binary logistic regression confirmed that high serum IGF-I was associated with increased prevalence of AD [adjusted Odds Ratio (OR) = 1.83, 95% confidence interval (CI): 1.005-3.32 per standard deviation (SD) increase in serum IGF-I]. This association was more robust after exclusion of patients receiving treatment with acetylcholinesterase inhibitors or N-methyl D-aspartate (NMDA) receptor antagonists (OR = 2.23, 95 % CI: 1.10-4.48). In the total study population (n = 76) as well in the AD group (n = 40), serum IGF-I correlated negatively with CSF Aβ1-42, and CSF IGF-I correlated positively with CSF/serum albumin ratio, CSF total tau, and CSF phosphorylated tau.

CONCLUSION

In AD patients without major brain vascular comorbidities, serum but not CSF levels of IGF-I were increased after correction for covariates. This association was strengthened by exclusion of patients receiving medical treatment. Overall, the results support the notion of IGF-I resistance in mild AD dementia.

Morphological changes in the central sulcus of children with isolated growth hormone deficiency versus idiopathic short stature

In this study, the morphological changes in the central sulcus between children with isolated growth hormone deficiency (IGHD) and those with idiopathic short stature (ISS) were analyzed. Thirty children with IGHD (peak growth hormone < 5 µg/L) and 30 children with ISS (peak growth hormone > 10.0 µg/L) were included. Morphological measurements of the central sulcus were obtained from T1-weighted MRIs using BrainVISA, including the average sulcal width, maximum depth, average depth, top length, bottom length, and depth position-based profiles (DPPs). The bilateral average width of the central sulci was significantly wider, while the left maximum depth and right average depth of the central sulcus were significantly smaller, in children with IGHD than in children with ISS. There were no significant differences in the right maximum depth, left average depth, or bilateral top length and bottom length of the central sulcus between groups. The DPPs of the middle part of both central sulci (corresponding to the hand motor activation area) and the inferior part of the right central sulcus (corresponding to the oral movement area) near the Sylvian fissure were significantly smaller in children with IGHD than in controls before false discovery rate (FDR) correction. However, all the above significant DPP sites disappeared after FDR correction. There were significant morphological changes in the three-dimensional structure of the central sulcus in children with IGHD, which were the outcome of other more essential cortical or subcortical changes, resulting in their relatively slower development in motor, cognitive, and linguistic functional performance.

Morphological changes of the cerebral cortex between children with isolated growth hormone deficiency and idiopathic short stature

The growth hormone (GH)-insulin-like growth factor-I (IGF-I) axis plays an important role in normal brain development, and GH deficiency inevitably affects the growth of the cerebral cortex. This study was designed to analyze morphological differences in gray matter volume, cortical surface area, and gray matter thickness between children with isolated growth hormone deficiency (IGHD) and children with idiopathic short stature (ISS). Twenty-four children with IGHD (mean age 9.42 years, peak GH < 5 μg/l) and 24 controls with ISS (mean age 9.21 years, peak GH > 10 μg/l) were included. High-resolution three-dimensional T1-weighted MRIs were acquired at participants' first visit. Measurements of gray matter volume, cortical surface area and gray matter thickness were obtained using FreeSurfer. The total and regional differences between groups were statistically analyzed. Correlations between the FreeSurfer results and GH and IGF-I levels were also obtained. The gray matter volume, cortical surface area and gray matter thickness of the total brain and of the bilateral hemispheres of children with IGHD were significantly smaller than those of children with ISS (all P values < 0.05). All the measurements had similar cortical distributions between groups but varied across regions. Cortical regions with significant differences in the mean gray matter volume and surface area were mainly distributed around the bilateral central sulci and the lateral and basal parts of the temporal lobes (all P values < 0.05). There were negative correlations between gray matter volume, cortical surface area and GH levels, and the right hemispheric and total cortical surface area correlated significantly with GH levels (all P values < 0.05) in children with IGHD. There were significant positive correlations between gray matter volume, cortical surface area and IGF-I levels (all P values < 0.05) in both groups, except for in left hemispheric gray matter volume in children with ISS. Children with IGHD have significant morphological changes in the cerebral cortex, which were partially influenced by GH and IGF-I levels. These cortical changes may be related to deficits in their relatively slower development in intelligence, motor performance, and other functions.

Neuroprotective Biomarkers and Cognitive Function in a Long-Term Prospective Population-based Study of Aging US Adults

BACKGROUND

Relationships between brain-derived neurotrophic factor (BDNF), insulin-like growth factor (IGF-1), aldosterone, and cognition in aging were evaluated in the population-based Epidemiology of Hearing Loss Study (1993 to present).

METHODS

Beginning in 1998 to 2000, cognitive impairment was assessed by report of physician diagnoses and the Mini-Mental State Examination. In 2009 to 2010 and 2013 to 2016, information was collected on diagnosis of mild cognitive impairment/dementia. Decline in cognitive function was assessed by principal component analysis from additional tests administered during 2009 to 2010 and 2013 to 2016. BDNF, IGF-1, and aldosterone were measured in serum collected in 1998 to 2000.

RESULTS

There were 1970 participants (mean age=66.9 y; 59.1% female) without cognitive impairment at baseline. Among women, low BDNF was associated with 16-year incident cognitive impairment [hazard ratio=1.76; 95% confidence interval (CI)=1.04, 2.98]. Among men, increasing IGF-1 was associated with decreased risk [per SD: relative risk (RR)=0.57; 95% CI=0.35, 0.92], whereas increasing aldosterone levels were associated with increased risk (per SD: RR=1.28; 95% CI=1.01, 1.62) for 5-year incident mild cognitive impairment/dementia. Overall, low BDNF was associated with increased risk (RR=1.52; 95% CI=1.02, 2.26) for 5-year cognitive decline.

CONCLUSION

Low levels of serum BDNF and IGF-1 were associated with poorer cognition during aging. There may be differential biomarker effects by sex.

Serum insulin-like growth factor 1 (IGF-1) in multiple sclerosis: relation to cognitive impairment and fatigue

Background

Multiple sclerosis (MS) is a chronic demyelinating central nervous system (CNS) disease. Changes in insulin growth factor 1 (IGF-1) input to the brain can affect survival of myelin and CNS cells. The study aims to investigate the relation of serum IGF-1 levels with cognitive impairment and fatigue in MS patients.

Methods

This study was conducted on 46 MS patients and 46 healthy controls. All participants were subjected to clinical assessment, serum IGF-1 levels, expanded disability status scale (EDSS), modified fatigue impact scale (MFIS), and Montreal cognitive assessment (MoCA) scale.

Results

There was no significant difference between patients and controls regarding serum IGF-1 levels (P = 0.19). However, low serum levels of IGF-1 have significantly greater odds for fatigue (P = 0.002) and cognitive impairment (P < 0.001). Also, serum IGF-1 levels have a significant negative correlation with MFIS (r = - 0.701 and P < 0.001) and a significant positive correlation with MoCA scale (r = + 0.84 and P < 0.001).

Conclusions

The results, specifically that low levels of serum IGF-1 was associated with cognitive impairment and fatigue in MS, suggest that IGF-I may be involved in the pathogenesis of cognitive deficits and fatigue in MS disease.

Insulin-like Growth Factor 1 (IGF-1) as a marker of cognitive decline in normal ageing: A review

Insulin-like Growth Factor 1 (IGF-1) and its signaling pathway play a primary role in normal growth and ageing, however serum IGF-1 is known to reduce with advancing age. Recent findings suggest IGF-1 is essential for neurogenesis in the adult brain, and this reduction of IGF-1 with ageing may contribute to age-related cognitive decline. Experimental studies have shown manipulation of the GH/GF-1 axis can slow rates of cognitive decline in animals, making IGF-1 a potential biomarker of cognition, and/or its signaling pathway a possible therapeutic target to prevent or slow age-related cognitive decline. A systematic literature review and qualitative narrative summary of current evidence for IGF-1 as a biomarker of cognitive decline in the ageing brain was undertaken. Results indicate IGF-1 concentrations do not confer additional diagnostic information for those with cognitive decline, and routine clinical measurement of IGF-1 is not currently justified. In cases of established cognitive impairment, it remains unclear whether increasing circulating or brain IGF-1 may reverse or slow down the rate of further decline. Advances in neuroimaging, genetics, neuroscience and the availability of large well characterized biobanks will facilitate research exploring the role of IGF-1 in both normal ageing and age-related cognitive decline.

Circulating insulin-like growth factor 1 and insulin-like growth factor binding protein-3 level in Alzheimer's disease: a meta-analysis

It has been reported that the associations between circulating insulin-like growth factor-1 (IGF-1) and insulin-like growth factor binding protein-3 (IGFBP-3) and Alzheimer's disease (AD) are controversial. Thus, present meta-analysis was carried out to confirm the probable associations. We searched "PubMed", "Springer" and "Medline" databases using the term ("insulin-like growth factor-1" or "IGF-1" or "insulin-like growth factor binding protein-3" or "IGFBP-3") and ("Alzheimer's disease") until April 2016. Furthermore, standard mean differences (SMDs) were calculated. A total of seven reports involving 1342 percipients were pooled. SMDs were -0.25 (P = 0.22) and -0.33 (P = 0.08) for IGF-1 and IGFBP-3, respectively. Furthermore, the circulating IGF-1 levels in AD patients were lower than controls when studies with the difference of mean age ≤1 year (SMD -0.57, P = 0.007) or 2 years (SMD -0.58, P = 0.02) or difference of mean MMSE scores ≤10 scores (SMD -0.94, P < 0.00001), or studies from Europe (SMD -0.89, P < 0.00001) were excluded. In addition, the circulating IGFBP-3 levels in AD patients were lower than controls when studies with the difference of mean age ≤2 years (SMD -0.62, P = 0.006) or difference of mean MMSE scores ≤6 scores (SMD -0.48, P = 0.0004), 7 scores (SMD -0.58, P = 0.02), or 8 scores (SMD -0.80, P = 0.03) were excluded. Even though no significant difference of circulating IGF-1 and IGFBP-3 levels in AD patients comparing with controls was found in present meta-analysis, the current study provided the evidence that the circulating IGF-1 and IGFBP-3 level in AD patients were influenced by the difference of mean age as well as MMSE scores. Furthermore, circulating IGFBP-3 levels in AD patients may be decreased earlier than IGF-1.